Rheological Fluids for Particle Removal

ABSTRACT

Methods and apparatus for cleaning a substrate (e.g., wafer) in the fabrication of semiconductor devices utilizing electrorheological (ER) and magnetorheological (MR) fluids to remove contaminant residual particles from the substrate surface are provided.

CROSS REFERENCE TO RELATED APPLICATION

This application is a division of U.S. Ser. No. 12/035,008, filed Feb.21, 2008, now U.S. Pat. No. 7,981,221, the entire content of which isincorporated by reference herein.

TECHNICAL FIELD

Embodiments of the invention relate to the cleaning of surfaces in thefabrication of semiconductor and integrated circuit devices.

BACKGROUND OF THE INVENTION

Various methods and aqueous cleaning solutions have been used for theremoval of small residual particles and contaminants from surfaces, suchas a wafer surface in the fabrication of semiconductor-based structuresand devices. A post-process clean is typically conducted to removeresidual particles remaining on the surface after a processing step suchas etching, planarization, polishing, sawing, film deposition, etc.,prior to performing another device fabrication step such as ametallization, gate or device formation, etc. If residues orcontaminants remaining from a process step are not effectively removed,various fabrication problems and defects in the finished integratedcircuit device can arise. For example, conductive residual particles(i.e., metals) that remain on a surface feature can cause such problemsas shorts between capacitor electrodes or other electrical failures, andnon-conductive contaminants on a feature such as particles (e.g., SiO₂,polysilicon, nitride, polymers, etc.) from a chemical mechanicalplanarization or polishing (CMP) or other process can cause problemssuch as the failure in adhesion of subsequent layers, a loss of criticaldimension of the formed feature, or pattern deformation in that arealeading to yield loss. Current technology nodes (e.g., 65 nm andsmaller) require a high level of surface cleaning, including the removalof remnant particles while maintaining other surface° materials intact.At each technology node, the presence of ¼-pitch remnant particles isconsidered to be a yield inhibitor.

A widely used cleaning technique to remove surface materials is an RCAclean which conventionally includes first applying an aqueous alkalinecleaning solution known as a Standard Clean 1 (SC1) to remove particlecontaminants, which consists of a dilution of ammoniumhydroxide/hydrogen peroxide (NH₄OH/H₂O₂) followed by a deionized (DI)water rinse. To remove metal contaminants, an aqueous acidic cleaningsolution known as a Standard Clean 2 (SC2) composed of a hydrochloricacid/hydrogen peroxide (HCl/H₂O₂) dilution is often applied, followed bya second DI water rinse. Other wet cleaning methods used for cleaningresidues from structures include, for example, a piranha clean using asulfuric acid based mixture (e.g., H₂SO₄/H₂O₂), a buffered oxide etchsolution, and fluorine-based aqueous chemistries.

The small particles or contaminants resulting from fabrication steps areheld to a surface such as by electrostatic forces and become entrenched,typically require relatively large forces to remove them. Cleaningsolutions are often applied in conjunction with acoustic energy (i.e.,ultrasonic or megasonic energy), high pressure spraying techniques,mechanical scrubbing techniques with a pad or brush, etc. to enhance thecleaning action of the solution to remove materials and dislodgeparticles from the wafer surface. However, acoustic cleaning andspraying techniques apply forces in all directions, which can damagesensitive structures or alter critical dimensions without effectivelyremoving all of the particulate contaminants from the substrate. Inaddition, many cleaning solutions can attack and/or dissolve thestructures formed in the fabrication step.

It is difficult to get acceptable particle removal from a substratesurface without adversely affecting fabricated structures or othersurface materials using conventional technologies.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention are described below with reference to thefollowing accompanying drawings, which are for illustrative purposesonly. Throughout the following views, the reference numerals will beused in the drawings, and the same reference numerals will be usedthroughout the several views and in the description to indicate same orlike parts.

FIG. 1 is a diagrammatic, elevational, cross-sectional view of anembodiment of an apparatus according to the invention for applying anelectrorheological (ER) fluid to remove particles from a substrate.

FIG. 2 is an isometric view of the apparatus shown in FIG. 1, takenalong lines 2-2.

FIG. 3 is an elevational, cross-sectional view of a substrate at apreliminary processing stage according to an embodiment of the presentdisclosure.

FIGS. 4-8 are cross-sectional views of the substrate of FIG. 3 atsubsequent processing steps according to an embodiment of the invention.

FIG. 9 is an elevational, cross-sectional view of a substrate at apreliminary processing stage according to another embodiment of thepresent disclosure.

FIGS. 10-11 are cross-sectional views of the substrate of FIG. 9 atsubsequent processing steps.

DETAILED DESCRIPTION OF THE INVENTION

The following description with reference to the drawings providesillustrative examples of devices and methods according to embodiments ofthe invention. Such description is for illustrative purposes only andnot for purposes of limiting the same.

In the context of the current application, the term “semiconductorsubstrate” or “semiconductive substrate” or “semiconductive waferfragment” or “wafer fragment” or “wafer” will be understood to mean anyconstruction comprising semiconductor material, including but notlimited to bulk semiconductive materials such as a semiconductor wafer(either alone or in assemblies comprising other materials thereon), andsemiconductive material layers (either alone or in assemblies comprisingother materials). The term “substrate” refers to any supportingstructure including, but not limited to, the semiconductive substrates,wafer fragments or wafers described above. The phrase“electrorheological (ER) effect” refers to the abrupt change inviscosity in certain suspensions upon application of an electric field.

Embodiments of the present invention relate to methods of cleaning asubstrate (e.g., wafer) in the fabrication of semiconductor devicescomprising a particle removal process utilizing a fluid that changesviscosity in the presence of an external electric or magnetic field(“rheological fluid”), including electrorheological (ER) andmagnetorheological (MR) fluids. Generally, both ER and MR fluids can becomposed of a carrier fluid, particles, surfactants and additives. Theinvention provides the ability to use minimal force for shearingparticles from a substrate without damaging fragile structures andfeatures.

In some embodiments of the invention, an electrorheological (ER) fluidis applied, which are fluids that can reversibly undergo a change inrheological (flow) properties (i.e., apparent viscosity) upon theapplication of a sufficiently powerful electric field, switching from anormal fluid or liquid state to a highly viscous, plastic or semisolidto a solid consistency upon application of an electric field, and backto a fluid state when the electric field is turned off. Generally, theelectric field can be either an alternating current (AC), pulsed directcurrent (DC), or DC, with AC producing less electrophoresis of particlesto electrodes. In general, the apparent viscosity of an ER fluidincreases in proportion to the strength of an electric field.

In some embodiments, the ER fluid is a heterogeneous dispersion composedof finely divided solids or particles suspended in a non-conducting,electrically insulating carrier or base liquid (e.g., oil) or liquidmixture of low dielectric constant (k). The base liquid is hydrophobic(i.e., totally immiscible in water) and compatible with the materials tobe treated, and has a suitable chemical and thermal stability over thetemperature range of the application. In embodiments of the invention,the base liquid has a wide temperature range with a low freezing pointand a high boiling point (e.g., from about −40° C. to about +200° C.)and a relatively low density. To avoid sedimentation and settling ofsolids, the base liquid should have a density about equal to the densityof the particles. The ER fluid has a suitably low viscosity at roomtemperature (25° C.) in the absence of an electric field to incorporatea suitable and effective amount of the particulate phase into the fluidphase, e.g., less than about 10 pascal-second (Pa·s), or about 0.1-0.3Pa·s (about 1-3 poise (P)) but a very high viscosity when subjected toan electric field such that the viscosity is no longer measurable with anear zero rate of flow.

Examples of materials utilized for particle dispersion type ER fluidthat can be utilized in embodiments of the invention are described, forexample, in U.S. Pat. No. 5,879,582 (Havelka et al.) and US 2007/0023247(Ulicny) (fluid phase), the disclosures of which are incorporated byreference herein.

Insulating base liquids that can be used in the ER fluid include, forexample, silicone oils such as polyalkyl-, polyaryl-, polyalkoxy-, orpolyaryloxysiloxane oils and silicate oils (e.g., polydimethylsiloxanes, liquid methyl phenyl siloxanes, tetraethyl silicate, etc.);mineral oils; vegetable oils (e.g., sunflower oils, rapeseed oil andsoybean oil); hydrocarbon oils including paraffin oils, naphthalenes,chlorinated paraffins, olefin oligomers and hydrogenated olefinoligomers such as polyisobutylene, ethylene-propylene copolymers, etc.);polyphenylethers; polyesters such as perfluorinated polyesters, dibasicacid esters and neopentylpolyol esters; phosphate esters; glycol estersand ethers such as polyalkylene glycol; aromatic-type oils such asbenzoic acid, phthalic acid, etc.; alkylene oxide polymers andinterpolymers, and derivatives thereof such as methyl-polyisopropyleneglycol; carbon tetrachloride; and chlorofluorocarbons.

The ER particles incorporated into the liquid phase of the ER fluid arecapable of exhibiting electrorheological activity (i.e., electricallypolarizable). The ER particles can be composed, for example, ofinorganic materials such as silica, titanium oxide (TiO₂), mica, talc,glass, alumina, magnesium silicate, aluminosilicates, zeolites, etc.;polymeric materials including polymeric salts, poly(lithiummethacrylate), poly(sodium styrene sulfonate), etc.; carbohydrate-basedparticles and related materials such as starch, flour, monosaccharides,and cellulosic materials; metal hydroxides activated with water or polarsolvent; and carbonaceous particles (e.g., as described in U.S. Pat. No.6,797,202). In another embodiment, the particles can be coated with apolymer, for example, polymer-coated iron magnetite. Examples ofcellulosic materials include cellulose and cellulose derivatives such asmicrocrystalline cellulose, amorphous cellulose, cellulose ethers andesters (e.g., methylcellulose, ethyl cellulose, hydroxyethyl cellulose,hydroxypropyl cellulose, cellulose nitrates, sodium carboxymethylcellulose, cellulose propionate, cellulose butyrate, etc.), cellulosephosphates, chitin, chitosan, chondroiton sulfate, natural gums such aszanthan gum, cellulose xanthate, and the like.

An activator substance such as amines and organic compounds (e.g.,thiols, carboxylic acids, etc.) that form hydrogen bonds or anintrinsically ER-active material such as polyaniline or other conductivepolymer, can be optionally applied to the surface of the particles tocontrol the surface conductivity of the particles and enhance the EReffect. In other embodiments, the ER particles can be coated with apolymer such as polystyrene (PS), polymethacrylate (PMMA) orpolyvinylpyrrolidone (PVP), and functionalized with carboxylic or aminegroups to form a charged surface on the ER particles that is the same asthe substrate such that the ER particles are repelled by the substrateand easier to remove.

The ER particles can be in the form of a powder, fibers, spheres, rods,core-shell structures, and the like. The ER particles can also bedesigned to be plate-shaped such that shear is due to the lever action.The size and shape(s) of the ER particles can be varied according toresidual particles to be removed, and for effective substrate cleaningand removal of residual particles without damaging the substrate or thestructures and materials on the substrate. Generally, the ER particleswill have a size (e.g., diameter) that is larger than the residualparticles to be removed from the substrate. In embodiments of theinvention, the size of the ER particles are larger than the residualparticles by a factor of about 10, i.e., about ten times (10×) the sizeof the residual particles to be removed. In some embodiments, the sizeof the ER particles can be over a range of about 0.1-100 μm, e.g., about1-60 μm, about 10-30 μm, etc. For example, to remove contaminantresidual particles with a diameter of about 5-10 μm, the averageparticle size of the ER particles can be about 50-100 μm. As anotherexample, where residual particles are smaller at about 0.05-2 μm, the ERparticles can be about 0.5-20 μm in size (i.e., 10× larger).

The volume fraction (concentration) of ER particles in the ER fluidshould be sufficient to provide the desired electrorheological effect orperformance at the applied electric field. The concentration of ERparticles is such that the particles can be maintained as a dispersionin the base fluid but not so high that sedimentation or settling occurs,and low enough to allow the ER fluid to maintain a relatively lowviscosity for handling in the absence of an applied field (zero-fieldviscosity). In embodiments of the invention, the ER particles can beincluded in the ER fluid at a concentration over a range of about 2-90%by weight of the total composition, and in some embodiments at about60-80% by weight, about 20-60% by weight, about 30-50% by weight, etc.The weight percentages of the ER particles can be adjusted according tothe density of the fluid phase, and/or the density of the particles canbe matched with a base fluid for dispersion of particles within the ERfluid.

Optionally, the ER fluid can contain typically used additives including,for example, antioxidants, and surfactants or dispersing agents(dispersants) to increase the conductivity of the ER particles and tomaintain a uniform dispersion and prevent agglomeration of the ERparticles, at about 0.4-10% by weight of the fluid, or about 0.5-6% byweight. Surfactants can be added directly to the base liquid or as acoating on the surface of the ER particles. Examples of surfactantsinclude block copolymers dedecyl alcohol, fatty acids and amines,glycerol, glycerol esters, glycerol monooleates, hydrocarbon polymers,sodium oleate, tin oxide, among others. The ER fluid can also include alow molecular weight polar compound (dielectric constant (k) of greaterthan 5) as an activator that generally interacts with the particulatephase predominantly by hydrogen bonding to improve the flow propertiesand enhance the ER effect, at about 0.4-8% by weight, or about 0.3-5% byweight. Examples of polar compounds include water (up to about 20% byweight), amines (e.g., ethanolamine, ethylenediamine, etc.), amides,nitriles, alcohols, polyhydroxy compounds (e.g., ethylene glycol,glycerol, etc.), low molecular weight esters (e.g., ethyl acetate),carboxylic acids (e.g., acetic acid formic acid, trichloroacetic acid,etc.) and/or other electrolytes such as KCl, LiCl, LiNO₃, CH₃COONa,Mg(ClO₄)₂, NaCl, ZnCl₂, ZnSO₄, and other organic and inorganic salts ofmetal ions.

The properties of the ER fluid can be modified by varying the componentsand concentrations of the ER particles and the base liquid. Generallyincreasing the concentration of the particles in the fluid or increasingthe intensity of the electric field will increase the viscosity of theER fluid. The properties of the ER fluid can also be modified by the ERparticle size and density, the carrier or base fluid properties,additives and temperatures, for example.

The viscosity of the ER fluid can be determined according to knowntechniques, for example, using a viscometer. The viscosity of the ERfluid can be varied according to the base liquid that is used, from arelatively low viscosity base fluid such as isopropyl alcohol (IPA),acetone and propanol, to a relatively high viscosity base fluid such asan ethylene glycol/sulfuric acid mixture. The viscosity of the ER fluidcan also be varied by the type and concentration of the ER particles.For example, acetone having a relatively low no-field viscosity of about0.306 cP (at 25° C.) can be combined with silica-based ER particles at aconcentration of about 0.4-1% by weight to maintain a relatively lowviscosity ER fluid, or with titanate-based ER particles such asstrontium titanate at the same concentration to provide a higherviscosity ER fluid.

In other embodiments, the ER fluid can be formulated as a homogeneousfluid without particles, for example, as an oil-in-oil emulsion, orliquid crystal polymer dispersed in an insulating oil, such as polyvinylalcohol (PVA) in Vaseline oil, liquid crystalline polysiloxanes dilutedin polydimethylsiloxane (DMS), fluorine compounds in an electricallyinsulating medium, among others. Homogenous ER fluids are formulated tochange viscosity in response to an electric field, which can be utilizedto shear particles from a substrate surface. Examples of homogeneous ERfluids that can be utilized in embodiments of the invention aredescribed, for example, in U.S. Pat. No. 5,891,356 (Unoue et al.) andU.S. Pat. No. 5,374,367 (Edamura).

FIGS. 1-2 depict an embodiment of an apparatus, designated generally as10, which can be utilized in embodiments of the invention for applyingan ER fluid to a substrate (26) to be processed, which is a wafer in thepresent example. The apparatus 10 generally includes a containmentvessel 12 with a lid 12 a for receiving and containing an ER fluidtherein, an inlet 14 and an outlet 16 for passage of the ER fluid intoand out of the vessel 12, electrodes 18, 20 connected to a power source(shown schematically as 22 connected to two electrodes) to providepositive and negative potential, and a support 24 for a substrate 26(e.g., wafer).

The apparatus 10 can be connected to other processing units/systems, forexample by a conveyor mechanism (not shown) for conducting the substrate26 through a processing system, including a pre-cleaning apparatusand/or a post-cleaning apparatus (not shown). The various units can beelectrically coupled to a microprocessor, which may be programmed tocarry out particular functions as is known in the art. A pre-cleaningapparatus can be designed to physically loosen up particles from thesubstrate by means of undercutting or etching of the substrate, whichcan be performed, for example, by a Standard Clean 1 (SC1) clean ordilute hydrofluoric acid (DHF) clean, typically to a depth of about0.1-0.5 angstroms. This can serve to lower the shear forces required bythe ER fluids for cleaning. A post-cleaning can then be applied toremove the ER particles.

The containment vessel 12 and lid 12 a of the apparatus 10 can becomposed of an insulating material such as glass, plastic, andpolyvinylidene fluoride (PVDF), and define a parallel-plate channel forthe flow of the ER fluid. In the illustrated embodiment, a plurality ofmetallic strip electrodes 18, 20 are formed on the surface of thecontainment vessel 12 (or the lid) for generating an electric field, andextend transversely or parallel to the direction of flow of the ER fluid(arrow →). In the illustrated embodiment, the electrodes are situated onthe surface of the vessel to provide a parallel field configuration anda series of equidistantly spaced (e.g., an about 1 mm gap), alternatelynegative (−) and positive (+) charged electrodes (anode, cathode). Theelectrodes can be composed of a conductive metal or metal alloy, forexample, aluminum, silver, gold, titanium, tungsten, titanium-tungstenalloy, tantalum, platinum, copper, refractory metal silicide, or alloysthereof, or other suitable electrically conductive material. Theelectrodes can be formed on or embedded in the surface of thecontainment vessel 12 (or the lid), using known methods in the art, forexample, by chemical vapor deposition (CVD), screen printing,stenciling, electroplating, adhesive attachment of a foil or otherconductive material layer (e.g., copper foil about 100 μm thick), orother suitable method of attachment or formation.

The ER fluid is flowed (arrow →) into and through the containment vessel12 via inlet 14 and outlet 16. As the ER fluid is flowed between thefixed electrodes 18, 20, the flow properties of the ER fluid can becontrolled by application of a voltage between the electrodes. Theintensity of the applied voltage is generally in the range of about0.3-6 kV/mm (at 25° C.), or about 0.5-2.5 kV/mm. The applied voltage canbe a pulse voltage or continuous voltage.

The viscosity (stiffness) of the ER fluid increases when a voltage isapplied between the electrodes caused by the electric field. In theapplication of the ER fluid, power is generated to the electrodes toprovide an electric field of suitable intensity to control the flow ofthe ER fluid through the containment vessel 12 and the viscosity of theER fluid to shear residual particles in a lateral direction from thesurface of the substrate and trap the loosened residual particles withinthe ER fluid.

In embodiments of the method, the frequency (intensity) of the appliedenergy field between the electrodes 18, 20 can be adjusted andcontrolled to vary the viscosity of the ER fluid during the processingstep from a liquid phase to a semi-solid to a solid phase The viscosityof the ER fluid can be increased proportionally with the voltage/currentthat is applied. The intensity of the applied electric field can also becontrolled to vary the rate of change of the viscosity of the ER fluidfrom a liquid to a semi-solid material to effectively trap the residualparticles within the semi-solid ER fluid (which is subsequently removedfrom the substrate). A pulse voltage can be used to adjust and controlthe viscosity and flow of the ER liquid. In other embodiments, thefrequency of the electric field can be controlled or a pulse voltage canbe used to increase the viscosity of the ER fluid from a liquid/fluidstate to a semi-solid state to trap residual particles and back to afluid state to loosen and move residual particles away from lines orother structures situated on the surface, and lessen the pressureimposed upon the structures and allow the structures to relax, unlikethe force produced by other techniques such as megasonic or spraycleaning that cannot be readily controlled and modified.

In yet other embodiments, the polarity (+) or (−) of the electrodes 18,20 can be rapidly changed or pulsed (e.g., by applying a pulse voltage)to cause the ER particles to “rock” and to shear residual particles witha low force. This action provides significantly lower force on residualparticles than the actual adhesion force, and provides removal of theparticles/contaminants without damage to the structures (e.g., lines,etc.). In other embodiments, the field can be repeatedly varied torepeatedly alter the viscosity of the fluid, e.g., by cyclically orrepeatedly applying and terminating the field to increase and decreasethe viscosity of the ER fluid between a fluid consistency and asemi-solid consistency. The waveform of the applied field can beoptimized to remove the contaminant particles without damage of devicestructures. For example, resonant frequency of the device structure canbe avoided such that a damage free regime is found for contaminantremoval.

It is believed that under the influence of an external electric field,the initially unordered ER particles in a particle dispersion type ERfluid undergo dielectric polarization to orient and form a chain orcolumn structure between the electrodes, whereby shear stress (sheerresistance) of the ER fluid is increased resulting in an increase inviscosity of the ER fluid from a liquid state to a solid-like state. Thesolid ER fluid returns to liquid when the electric field is removed dueto the ER particles returning to an unorganized and suspended statewithin the base fluid. For homogeneous ER fluids, it is believed thatmolecules of the crystal phase material orient in one direction due tothe electric field, whereby shear stress of the ER fluid is increasedresulting in an increase in viscosity.

An embodiment of a method according to the invention for removingparticulate contaminants from a substrate 26 (e.g., wafer) is describedwith reference to FIGS. 3-8. The substrate 26 can comprise structuressuch as lines, DRAM, STI structures, contacts, containers and otherfeatures. As shown in FIG. 3, features such as lines 28 of a materialsuch as oxide, polysilicon, carbon, resist, or other hard mask material,have been fabricated on the substrate 26 according to a semiconductorprocessing step. Residual particles 30 such as oxide, nitride,polysilicon (silicon), carbon, polymer resist, metals (e.g., W, WSi_(x),TiN, etc.) etc., remain adhered to the surface 32 of the substrate. Thecomposition of the substrate 26 and the residual particles 30 will, atleast in part, determine the ultimate strength of the adhesion of theresidual particles to the substrate surface 32.

In a preliminary step shown in FIG. 3, a conventional pre-cleanprocedure using a cleaning solution (arrows ↓) comprising, for example,citric acid, ammonium fluoride, surfactants, phosphoric acid, sulfuricacid, hydrofluoric acid, or an ammonia-peroxide mixture (e.g., SC1clean), can first be conducted to loosen and displace the residualparticles 30 from attachment to the substrate surface 32 by etching aportion of the substrate, followed by a rinse (e.g., DI rinse).Following the pre-clean step, loosened residual particles 30 remainattached to the substrate surface 32, as depicted in FIG. 4.

As illustrated in FIG. 5, the substrate 26 is then placed into anapparatus 10 as described, for example, with reference to FIGS. 1-2, forapplication of an ER fluid to remove remaining residual particles fromthe surface of the substrate. With the substrate 26 positioned on thesupport 24, an ER fluid 34 can be introduced into the containment vessel12, which, in the illustrated embodiment is composed of ER particles 36dispersed in a carrier or base fluid 38. Typical process parameters forapplying the ER fluid include an ER fluid temperature and a substrate(wafer) temperature of about 20-27° C., or about 30-50° C.

In the application of the ER fluid 34, power is generated to theelectrodes 18, 20 as shown in FIG. 6, to generate an electric field(arrows ↑↑) of suitable intensity to cause the viscosity of the ER fluid34 to increase and trap the loosened residual particles 30 within the ERfluid. As depicted in FIG. 6A, under the influence of the externalelectric field, the unordered particles 36 orient and attract each otherto form particle chains in the fluid along the field lines (arrow E) andprovide a shear force over the surface 32 of the substrate 26. Due tothe pre-clean application of the cleaning fluid and rinse (FIG. 3), theamount of shear force required in the application of the ER fluid toremove the residual particles 30 can be reduced significantly comparedto conventional forces such as megasonic energy or spraying, and interms of the force applied to contaminants 30 versus device structures28 to enable damage-free cleans.

The field is then turned off causing the ER fluid 34 to revert to aliquid form with the ER particles 36 and residual/contaminant particles30 suspended within the fluid, as illustrated in FIG. 7. The ER fluid 34containing the residual particles 30 can then be removed from thesubstrate 26, for example, by applying a rinse water or other aqueousmedium (arrows ↓40) under non-damaging conditions by dispensing, byaerosol spraying, or by megasonic rinsing.

As illustrated in FIG. 8, after removal of the ER fluid 34, a post cleanprocedure (arrows ↓↓) can be conducted, to remove remnants of the ERfluid 34 including residual particles 30 or ER particles 36 that remainon the substrate surface 32. The ER particles 36 generally have a largerdiameter than the residual particles 30 and can be readily removed, forexample, through the use of an SC1 clean or DHF clean (e.g., about 500:1water:HF) in conjunction with a spray or megasonic system, followed bywater rinse. In embodiments in which the ER particles 36 are coated witha polymer (e.g., PMMA, PVP, PS, etc.) and functionalized with a reactivegroup (e.g., carboxylic or amine group) which provides a charged surfacethat is the same as the substrate, the ER particles 36 are repelled bythe surface and easier to remove by rinsing.

Application of the ER fluid traps and effectively removes the residualparticles leaving a cleaned surface 32, as depicted in FIG. 8, whilemaintaining and preserving the integrity of the lines 28 (or otherstructure) present on the substrate 26. Subsequent processing of thesubstrate and features may then be conducted as known in the art.

In another embodiment of the invention illustrated in FIGS. 9-11, amagnetorheological (MR) fluid can be used to removeparticulates/contaminants from the substrate. MR fluids are fluids thatundergo a rapid increase in viscosity in the presence of a magneticfield, which is reversible. MR fluids are composed of a suspension ofmagnetic or magnetizable particles in an base or carrier fluid such asthe base liquids described herein for the ER fluids, e.g., a hydrocarbonoil, silicone oil, etc.

The magnetizable (MR) particles of an MR fluid are typically composed ofmagnetically soft ferro- or ferromagnetic or paramagnetic compounds. TheMR particles can be in the form of a powder, fibers, spheres, rods,plates, core-shell structures, and the like. Examples of magnetizableparticles include particles composed of materials such as iron, ironoxide, iron nitride, iron carbide, carbonyl iron, chromium dioxide, lowcarbon steel, silicon steel, nickel, cobalt, etc., or a combination oralloys of such materials (e.g., Fe—Co alloys, Fe—Ni alloys, Mn—Znferrite, Ni—Zn ferrite), and ceramic ferrites. In other embodiments, theMR particles are magnetic composite particles with a polymer core (e.g.,polystyrene-acetoacetoxyethyl methacrylate (PS-AAEM)) coated with amagnetic material (e.g., magnetite), as described, for example, in Choiet al., IEEE Transactions on Magnetics 41(10): 3448-3450 (2005). Inother embodiments, the MR particles are composed of a magnetic materialcore (e.g., magnetite) coated with a polymer material (e.g.,styrene-divinylbenzene copolymer). See, for example, US 2007/0023247 toUlicny et al., and U.S. Pat. No. 5,382,373 to Carlson et al., and U.S.Pat. No. 6,682,660 to Sucholeiki et al.

The size and shape(s) of the MR particles can be varied, as describedwith respect to the ER fluid, according to residual particles to beremoved, and for effective substrate cleaning and removal of residualparticles without damaging the substrate or the structures and materialson the substrate. The MR particles will generally have a size (e.g.,diameter) that is larger than the residual particles to be removed fromthe substrate, and in embodiments of the invention, the size of the MRparticles is larger than the residual particles by a factor of about 10(i.e., about ten times (10×) the size of the residual particles). Insome embodiments, the size of the MR particles can be over a range ofabout 0.1-100 μm, e.g., about 1-60 μm, about 10-30 μm, etc. For example,to remove contaminant residual particles with a diameter of about 5-10μm, the average particle size of the MR particles can be about 50-100μm. As another example, where residual particles are smaller at about0.05-2 μm, the MR particles can be about 0.5-20 μm in size (i.e., 10×larger).

The volume fraction (concentration) of ER particles in the ER fluidshould be sufficient to provide the desired magnetorheological effect orperformance at the applied magnetic field. The concentration of MRparticles is such that the particles can be maintained as a dispersionin the base fluid but not so high that sedimentation or settling occurs,and low enough to allow the MR fluid to maintain a relatively lowviscosity for handling in the absence of an applied field (zero-fieldviscosity). Generally, the concentration of MR particles in the MR fluidcan be over a range of about 2-90% by weight of the total composition,and in some embodiments at about 60-80% by weight, about 20-60% byweight, about 30-50% by weight, etc. The weight percentage of the MRparticles can be adjusted according to the density of the fluid phase,and/or the density of the particles can be matched with a base fluid fordispersion of particles within the MR fluid.

The MR fluid can optionally include additives such as those describedherein for the ER fluid, for example, surfactants and silica compositesto enhance the dispersion stability of the MR fluid againstsedimentation and aggregation of the MR particles.

An embodiment of a MR fluid apparatus 10′ is illustrated in FIG. 9,which includes a magnetic field generator 42′, which can be a magnet oran electromagnet (connected to a power source (not shown)), to activatethe MR fluid 34′. The apparatus 10′ also includes a containment vessel12′ (shown with a lid 12 a′) for containing the MR fluid 34′ with aninlet 14′ and an outlet 16′. In some embodiments, the apparatus 10′ (or10) can be designed such that the direction of the flow of therheological fluid is perpendicular to the field or flux lines. Aninsulator (not shown) can be used to block or shield the magnetic fieldgenerator 42′ and thereby inactivate the MR fluid to a viscous state.

Removal of particulate contaminants from a substrate using an MR fluidis similar to the above-describe processing using an ER fluid withreference to FIGS. 3-8. In brief, a substrate 26′ can undergo apre-clean step (FIG. 3) to loosen and displace the residual particles30′ from the substrate surface 32′. The pre-cleaned substrate 26′ canthen be placed into an MR apparatus, for example apparatus 10′ asillustrated in FIG. 9, and an MR fluid 34′ can be introduced into thecontainment vessel 12′. When an MR fluid is exposed to a sufficientlyhigh magnetic field (arrows →) from the magnetic field generator 42′,the magnetic MR particles 36′ within the MR fluid 34′ become polarizedand organize (coalesce) into chains or bands of particles in thedirection of the field or flux lines (e.g., as depicted in FIG. 6A),which acts to restrict the movement of the fluid and to increase theviscosity or flow resistance of the MR fluid, e.g., from a gel to a nearsolid or viscoelastic material. The MR particles 36′ and fluid 38′provide a shear force in a lateral direction over the substrate 26′ toloosen the residual particles 30′ from the surface 32′ and trap theparticles 30′ within the MR fluid. As depicted in FIG. 11, the MR fluid34′ can then be changed to a liquid form by turning off the magneticfield.

The MR fluid 34′ can be removed by rinsing with an aqueous medium (e.g.,water) (e.g., FIG. 7), and a post clean can then be conducted (FIG. 8)to remove remnant MR fluid including MR particles 36′ and residualparticles 30′ from the substrate, leaving a cleaned surface 32′.Subsequent processing of the substrate and features may then beconducted as desired.

Although specific embodiments have been illustrated and describedherein, it will be appreciated by those of ordinary skill in the artthat any arrangement which is calculated to achieve the same purpose maybe substituted for the specific embodiments shown. This application isintended to cover any adaptations or variations that operate accordingto the principles of the invention as described. Therefore, it isintended that this invention be limited only by the claims and theequivalents thereof. The disclosures of patents, references andpublications cited in the application are incorporated by referenceherein.

1. A semiconductor substrate having a surface with structures situatedthereon, and a rheological fluid in contact with the surface and saidstructures.
 2. The semiconductor substrate of claim 1, wherein therheological fluid comprises residual particles of said structuressuspended therein.
 3. The semiconductor substrate of claim 2, whereinthe rheological fluid is a viscoelastic, semi-solid consistency.
 4. Thesemiconductor substrate of claim 2, wherein the structures comprise amaterial selected from the group consisting of oxide, polysilicon,nitride, carbon and polymer resist.
 5. The semiconductor substrate ofclaim 2, wherein the residual particles are selected from the groupconsisting of oxide, nitride, silicon, carbon, polymeric, andmetal-comprising particles.
 6. The semiconductor substrate of claim 1,wherein the rheological fluid is an electrorheological fluid.
 7. Thesemiconductor substrate of claim 1, wherein the electrorheological fluidcomprises electrorheological particles dispersed within an insulatingfluid.
 8. The semiconductor substrate of claim 1, wherein theelectrorheological particles comprise a surface with an activatormaterial thereon, the activator material comprising an organic compoundor amine capable of forming hydrogen bonds.
 9. The semiconductorsubstrate of claim 1, wherein the electrorheological particles comprisea surface with a conductive polymer applied thereon.
 10. Thesemiconductor substrate of claim 1, wherein the electrorheologicalparticles are coated with a polymer selected from the group consistingof polystyrene, polymethacrylate and polyvinylpyrrolidone, said polymerfunctionalized with carboxylic or amine group.
 11. The semiconductorsubstrate of claim 1, wherein the electrorheological fluid comprises aliquid crystal polymer dispersed in an insulating fluid.
 12. Thesemiconductor substrate of claim 1, wherein the electrorheological fluidcomprises a homogenous fluid without electrorheological particles, saidhomogenous fluid selected from the group consisting of polyvinyl alcoholin oil, and liquid crystalline polysiloxane in polydimethylsiloxane. 13.The semiconductor substrate of claim 1, wherein the rheological fluid isa magnetorheological fluid.
 14. The semiconductor substrate of claim 1,wherein the magnetorheological fluid comprises magnetorheologicalparticles composed of a polymer core coated with a magnetic material.15. The semiconductor substrate of claim 1, wherein themagnetorheological fluid comprises magnetorheological particles composedof a magnetic material core coated with a polymer material.
 16. Anapparatus for cleaning a surface of a substrate, comprising: a vesselfor receiving and containing a rheological fluid therein; a fieldgenerator situated proximally to the vessel such that the field can begenerated to a fluid contained within the vessel; and a support for asubstrate situated within the vessel.
 17. The apparatus of claim 16,wherein the field generator comprises a negative charged strip electrodeand a positive charged strip electrode connected to a power source forsupplying a voltage to the electrodes.
 18. The apparatus of claim 17,wherein the electrodes are situated on a surface of the vessel andextend transversely to a direction of flow of an electrorheologicalfluid through the vessel.
 19. The apparatus of claim 17, wherein aplurality of equidistantly spaced and alternately negative and positivecharged strip electrodes are situated proximally to the vessel.
 20. Theapparatus of claim 16, wherein the field generator is operable torepeatedly apply and terminate the field.
 21. The apparatus of claim 16,wherein the field generator is operable to cyclically apply andterminate the field.
 22. The apparatus of claim 16, wherein the fieldgenerator is operable to repeatedly vary the field.
 23. The apparatus ofclaim 16, wherein the field generator is operable to repeatedly increaseand decrease the field.
 24. The apparatus of claim 16, wherein the fieldgenerator is operable to apply a pulse voltage.
 25. The apparatus ofclaim 16, wherein the vessel further comprises an inlet and an outletfor passage of the rheological fluid into and out of the vessel.
 26. Theapparatus of claim 16, wherein the vessel contains an electrorheologicalfluid.
 27. The apparatus of claim 16, comprising a magnetic fieldgenerator.
 28. The apparatus of claim 27, wherein the vessel contains amagnetorheological fluid.